This invention relates to rotational motion detectors and more specifically to a motion detector using a crystalline substance and acoustic wave energy in order to detect rate.
Conventional rate sensors include gyroscopes, ring lasers and nuclear magnetic resonance (NMR) devices. While each prior art device provides the same information, the different principles at which they operate result in different drawbacks, including cost, energy consumption, weight, and sensitivity. This results in each prior art device having different advantages and disadvantages, so that the selection of a particular rate sensor is dependent upon the particular application. For example, presently, most inexpensive rate sensors are mechanical gyroscopes, which use the gyroscopic forces of a rotating mass in order to provide an output of force required to turn the rotating mass about a gimbal having an axis generally perpendicular to the mass in the manner well known to those skilled in the art. Rate sensor information is used for a wide variety of applications in addition to mere detection of change in attitude of a vehicle. For example, a rate sensor may be used for sensing the direction of true north by sensing the spin axis of the earth's rotation.
Acoustic wave energy has been used in one prior art acoustic rate sensor design. In this prior art sensor, a transducer generating acoustic waves is physically separated from a rotating surface wave carrier. A drive means such as a motor, must rotate the surface wave carrier in order that rate can be measured by sensing interference patterns.
It is desirable to construct a rate instrument in such a way that relative movement of parts is not necessary. This has the advantage of eliminating costly drive and bearing components, as well as enhancing the accuracy and greatly extending the lifetime of the instrument. For this reason, it is desired to provide a low cost rate instrument in which relative movement of component parts is either not required or only required to a minimum extent. It is further desired that a no-moving part rate instrument be constructed in which sensing of rate is accomplished efficiently, and in a low cost manner. It is a further object of the invention to use acoustic wave sensing in a rate instrument which does not require moving parts.